One usage of these is in a secondary sort , which is used , when you want the output values from Map sorted (within a key).
You implement a KeyComparator and tell mapreduce to use it to order the keys using a composite key. To ensure that during partioning & Grouping , all the records for a key go to the same reducer you need to define and set a Partitioner and ValueGroupingComparator. search for Secondary Sort for more on this topic regards MJ On Fri, Aug 17, 2012 at 12:00 PM, Anbarasan Murthy <[email protected]> wrote: > Hi, > > I have a question in mapreduce api. > > Would like to know the significance of the following items under jobconf > class. > ValueGroupingComparator > KeyComparator > > > > Thanks, > Anbu. -- http://khangaonkar.blogspot.com/
